This invention generally relates to flexible containers, such as pouches, bags or other packages, having a reclosable plastic zipper. In particular, the invention relates to reclosable bags, pouches or other packages for containing vacuum, pressure or liquid.
To ensure hermeticity or airtightness, packagers have typically sealed their flexible containers to an extent that they are not reclosable after the seal is broken. Many flexible containers that were reclosable typically did not retain the desired vacuum, pressure or liquid containment feature that existed prior to the container being opened for the first time.
In many different applications, it is desirable to provide a reclosable container that, under normal or expected conditions of usage, will not leak fluid when the zipper is closed. Such a container should maintain a leakproof condition even when there is a large differential in pressure between the interior and exterior of the container. As used herein, the term “leakproof” does not mean free of leaks under all temperature/pressure conditions, but rather free of leaks over a range of temperatures and pressures expected to occur during normal usage of the reclosable container.
In the case of known collapsible, evacuable, zippered storage bags, the zipper is opened; an article is placed inside the bag; the zipper is closed, and then the bag is evacuated using a fixture that penetrates a bag wall. With the bag thus evacuated, a compressible article contained therein may be significantly compressed so that it is easier to transport and requires substantially less storage space. It is highly desirable that ambient air not leak into the evacuated interior space of the bag. Such leakage would cause a loss of vacuum. Also it is highly desirable that the zipper not open unintentionally due to mechanical forces that occur during bag manipulation.
Collapsible, evacuable storage bags are beneficial for reasons in addition to those associated with compression of the stored article. For example, removal of the air from the storage bag inhibits the growth of destructive organisms, such as moths, silverfish, and bacteria, which require oxygen to survive and propagate. Moreover, such bags, if properly sealed, are impervious to moisture, as a consequence of which the growth of mildew is inhibited.
Not only large, compressible items such as clothing may be stored in a collapsible, evacuable and reclosable storage bag. For example, it may be desirable to store bulk items made of small particles, such as powders or granulated resins, in an evacuated reclosable bag. The stored material may be of a type that, when exposed to air during storage, is rendered unsuitable for its intended purpose. If the reclosable bag were made leakproof, then the bulk contents inside the bag would not be exposed to air.
In accordance with another application, a reclosable storage bag may be filled at ambient atmosphere instead of being evacuated. If such a bag were placed under extremely low pressure, e.g., while being air-lifted via a cargo plane having a depressurized cargo bay, then a large differential in pressure would exist between the interior and exterior of the bag. In this situation, the internal pressure may be about 15 psi, while the external pressure is negligible. It is desirable that the bag not develop a leak and that the zipper not pop open under such conditions.
Another use for evacuable reclosable packages is in the field of food product packaging. After a package of food has been opened and a portion of the food product removed, the remaining food product can be stored by closing the reclosable feature and then evacuating the interior space of the package via a fixture that penetrates a package wall. It is highly desirable that such packages, containing perishable food product in a vacuum, be leakproof, i.e., hermetic. By preventing exposure to air, the life span of the perishable food product can be extended.
In other situations, it is desirable to provide a reclosable package capable of holding liquid without leaking during normal usage when the zipper is reclosed. Preferably such a package would be able to withstand a predetermined pressure differential (interior/exterior) without liquid leaking out of the package.
In a typical construction, a reclosable pouch, bag or other package has a plastic zipper comprising two extruded zipper strips, the ends of the zipper strips extending into the side seals of a flexible receptacle. Frequently, each zipper strip comprises a closure profile and a flange or fin portion (hereinafter “flange”). The zipper strips are joined to the web of web material by heat sealing the web to the zipper flanges. In order to facilitate the formation of a tight side seal, typically the ends of the zipper strips are crushed. During the crushing operation, heat and pressure are applied in sufficient amounts (e.g., by means of mutually opposing heated sealing bars) that the ends of the zipper strips soften or melt and then deform. The flattened ends of the zipper strips then fuse during cooling. This thermal crushing operation is typically done at a separate thermal crush station or as part of the formation of a side seal of the receptacle at a cross sealing station. This “thermal crushing” of the plastic zipper creates a transition between “as is” (i.e., not crushed) zipper and crushed zipper that is susceptible to the presence of leaks.
There is a continuing need for improvements in the construction of reclosable containers having a hermetic interior volume when the zipper is reclosed. In particular, there is a need for an improved reclosable container wherein leakage is eliminated in those areas of the zipper near the container side seals.